A major goal in the nonwovens industry is to reduce cost. At the same time there is growing concern in society about degradation of the natural environment. Disposal of solid waste is a major contribution to this growing environmental concern.
During the production of polypropylene nonwoven fabrics, significant waste polypropylene is generated during startup of the process, from trimming left when the nonwoven web is slit to customer's specification, and from rolls that may have been slightly damaged or otherwise out of specifications. This polypropylene waste, coming from previously spun polypropylene fiber and webs comprised of previously spun polypropylene fiber, can be safely sent to solid waste landfills. However since this is very clean polypropylene it can also be remelted for recycling back through the spunbonding process. Recycle thus meets two goals, saving of the cost of wasted polypropylene and reduced solid waste to downgrade the natural environment.
Recycling such polypropylene is well known in the nonwoven industry. However once the polypropylene goes through the spinning process it is partly degraded by oxidation so that the polymer molecular weight is reduced. This effect can be partly mitigated by the optimized addition of antioxidants. However some degradation is always seen. Such degradation can be seen by measuring the melt flow rate of the processed polymer. The melt flow rate will increase. The melt flow of polypropylene can be measured as taught in ASTM D-1238, at conditions of 230° C. and 2.14 kg.
Because of the reduced molecular weight, the recycled polypropylene is not generally suitable for being used by itself in the manufacture of spunbond nonwoven fabrics. Therefore, it is typically blended with virgin polypropylene. However, the amount of recycled previously spun polypropylene that can be recycled is limited. If too much recycled polypropylene is blended with the virgin resin, then an increase in the number of spinning breaks (broken filaments) will be seen. These broken filaments will cause quality defects in the finished spunbond nonwoven fabric or, in severe cases, a complete disruption of the manufacturing process. Second, the presence of too much recycled polypropylene can reduce the measured tensile strength of the resulting spunbond nonwoven fabric. For these reasons the amount of polypropylene recycled back through the process is usually limited to less than about 20% of the total polypropylene by weight.